In what ways is the word “work” as used in h2;u,er, ciji everyday language the same as that defined in physics? In what ways isie rc,h iu,;j2 it different? Give examples of both.

Can a centripetal force ever 8p4kjhuq n 28mdo work on an object? Explain.

Can the normal force on an object evezfcx fw;n1;(tu zuivzn:m2;2 r do work? Explain.

A woman swimming upstream is not moving with respect to1( rxjr+wfy 939y wcx2avhl4e the shore. Is she doing anyrcf9w94y(e r x j3x wlah+yv12 work? If she stops swimming and merely floats, is work done on her?

Is the work done by kinetic friction nayeg p15dl.* forces always negative? [Hint: Consider what happens to the dishegyda 51l.p ne*s when you pull a tablecloth out from under them.]

Why is it tiring to push hard against a solid wall even though you a*v a*5my7bymkp6pw3i re doing no woryapm v7b*wm *5k 6iyp3k?

You have two springs that are identical exc bm 08kavtghiw*/w/la. /*hlabix *5 yept that spring l is stiffer than spr ll/a5 ihyx mwawa //*i80gvk*.b tbh*ing 2 $(k_1>k_2).$ On which spring
is more work done $(a)$ if they are stretched using the same force, $(b)$ if they are stretched the same distance?

A hand exerts a constant horizontal force o ldm qz (,wuoc qj+.ji2-/*cawn a block that is free to slide on a frictionless surface (Fig.6-30). The blo +c(-qc dj,ozwm.lw auji/2*qck starts from rest at þoint A, and by the time it has traveled a distance $d$ to point B it is traveling withe bint $o$ point B it is traveling with speed $\nu_\mathrm{B}$.When the block has traveled another distance $d$ to point C, will its speed be greater than, less than, or equal to 2$\nu_\mathrm{B}$? Explain your reasoning

By approximately how much does your gravitational potential energy change sn+r/ qfy)s)2hbi3w9iyu8l qwhen you jump as high as you ca +us)s iq3y ni/fy)q wh2b9rl8n?

In Fig. 6–31, water balloons are tossed from the roof of a buildinxil66rf5j,hrfdz 1 b:g, all with the i6 ,fbr:6fdhx 51lrzj same speed but with different launch angles. Which one has the highest speed on impact? Ignore air resistance.

A pendulum is launched from a point that is a h(dg mgtflfqcn,ir2+c we38a07g kp;( eight h above its lowest point in two different ways (Fig. 6–32). During both launches, the pendulum is given an initial speed of 3.0m/s On the first launch, the initial velocity of the pendulum is diwn 8cc , ilgm g7 f0rfa;(tq2(3e+pgkdrected upward along the trajectory, and on the second launch it is directed downward along the trajectory. Which launch will cause it to swing the largest angle from the equilibrium position? Explain.

A coil spring of mass m rests upright on om:fjepu (;5l a table. If you compress the spring by pressing down with your hand and then release it, can the spring leave the table? Explain, u;u j(m f5:lpeosing the law of conservation of energy.

A bowling ball is hung from the ce*j:x+ nbsk(opzk 7+w 8y8jchviling by a steel wire (Fig. 6–33). The instructor pulls the ball back and stands agazjxk(8jcb n:8psoyw*k+vh 7 +inst the wall with the ball against his nose. To avoid injury the instructor is supposed to release the ball without pushing it. Why?

What happens to the gravitational potential energy eq6u:+ l5gw8t 4tscml when water at the top of a waterfall falls to the s:w 4tq6l mtglc5 ue8+pool below?

Describe the energy transformations when a child hops around on a pogo svecei-e ;:)v4tjh rmp y uw419tick.

Describe the energy transformations that take place when a swt*.uq xj*/y8 z2gnw.q tw5us kier starts skiing down w..qqujg s z/n*ywt* 8u5t2wx a hill, but after a time is brought to rest by striking a snowdrift.

A child on a sled (total mass m) starts from rest at the tx:vf:ul69bt8h b;, ixrzgml2 op of a hill of height h and slides down. Does the velocity at the bottom depend on the angle of the hill if (a) it is icy and there t9;gu,6mhb xv lf :r8xbl:2iz is no friction, and (b) there is friction (deep snow)?

Seasoned hikers prefer to step over a fallen log in their path rather than s2bp;7fcq3 h r. pbkw3otepping on top and jumping downh 37fw2 p. bq3kbopc;r on the other side. Explain.

Two identical arrows, one with twice the speed of th qm( j( xgsq*;j3/pxbme other, are fired into a bale of hay. Assuming the hay exerts a constant frixs jxp gqj(q(bmm*3; /ctional force on the arrows, the faster arrow will penetrate how much farther than the slower arrow? Explain.

Analyze the motion of a simple s2,wc d-w1 yl0lwrb py9winging pendulum in terms of energy, (a) ignoring friction, and (b) taking friction into account. Explain why a grandfather clock has to be woc ww0,2ybl1ld9wyr- p und up.

When a “superball” is dropped, can it rebound to a height greater than its ori gx5x;exs z+bsr-naoz fd6n1fa79z *1ginal height? Ex51o e7*fzsnrz ;-x1ad fn+x xsz6 9bagplain.

Suppose you lift a suitcase fr 95x bb.qh6mofom the floor to a table. The work you do on the suitca9xb bq6fohm5.se depends on which of the following: (a) whether you lift it straight up or along a more complicated path, (b) the time it takes, (c) the height of the table, and (d) the weight of the suitcase?

Repeat Question 22 for th8d gu luo4fv9;mbca,b:5 g.dn e power needed rather than the work.

Why is it easier to climb a mountain via a zigzagtz i7 m7vb0ayhj ej,1, trail than to climb straight up,tmyj hv 7j,0z1ie a7b?

Recall from Chapter 4, Example 4–14, that you can use a pulley and kp j/p5, a2gjwropes to decrease the force needed to raise a heavy load (see Fig. 6–34). But for ,w/jppgk5a j2 every meter the load is raised, how much rope must be pulled up? Account for this, using energy concepts.

  How much work is done by the gravitational force when6f8eh,4hps /tu6,jfrk f.w wx a 265-kg pile driver falls 2.80 m64 ,sfh,hfw etu.fwprj8k /6x ?    J

  A 65.0-kg firefighter climbar71um91q-zpr,ieyg2rwi *j s a flight of stairs 20.0 m high. How much work is required? ,1 a1er gir *iq7muyjw2r9pz-   J

  A 1300-N crate rests on the floor. How much work is required toino )(27i eslbr(ws yg:a 6yq. move it at constant speed (a) 4.0q)i.sge: 7wnlos (yb2r(yi 6a m along the floor against a friction force of 230 N,    J
(b) 4.0 m vertically?    J

  (I) How much work did the movers do (horizontally) pushin)d lq wz lnw.qsz6d* -ygx4(.xg a 160-kg crate 10.3 m across a rough floor without acceleration, if the effective coefficient of friction wanq.g ys * 6 -dlz(dwxxz)q.l4ws 0.50?    J

  A box of mass 5.0 kg is accelerated by a force across a floor at a rate of , r8yhr 1o/mco for 7.0 s. Find the net work d/m r o18ho,rcyone on the box.   J

  Eight books, each 4.3 cm thick with mass 1.7 kg, lie flat on a t+dkvfxvji:hhg2n m; 5l:+mp : able. How much work is required to stack them o ;2:+fjpx5vkvlmm+:h gn idh:ne on top of another?    J

A lever such as that shown in Fig. 6-35 can be used to liff objectch61c )di ch,ks we might not otherwise be able to liff. Show that the ratio of output force,dichch1)c k6 , $F_{\mathrm{O}}$, to input force, $F_{\mathrm{I}}$, is related to the lengths $\iota_\mathrm{I}$ and $\iota_\mathrm{o}$ from the pivot point by $F_{\mathrm{O}}/F_{\mathrm{I}}=l_{\mathrm{I}}/l_{\mathrm{O}}$ (ignoring friction and the mass of the lever), given that the work output equals work input.

  A 330-kg piano slides 3.6 m dowo:wqx* tge 3: md0kx1wn a 28° incline and is kept from accelerating by a man who is pushing back on it parallel to the incline (Fig. 6-36). The effective coefficient of kinetic friction is 0.40. Calculate:0gk o:1t3emxw*dx w :q
(a) the force exerted by the man,    N
$(b)$ the work done by the man on the piano,    J
$(c)$ the work done by the friction force,   J
$(d)$ the work done by the force of gravity,   J
$(e)$ the net work done on the piano   J

  (a) Find the force required to give a helicopter of mass M an accelerawne 3iies 606mtion of 0.166wms i0ene i30 g upward.    Mg
(b) Find the work done by this force as the helicopter moves a distance h upward.    Mgh

  $\text{What is the minimum work needed to push a 950-kg car 810 m up along a 9.0$^{\circ} $ incline? }$$(a)\text{ Ignore friction. }$    J
$(b)\\\text{Assume the effective coefficient of friction retarding the car is }0.25.$    J

  In Fig. 6-6a, assume the distance axis is li1:sh3 e*hy ewjy8d0nu/,n9 g tjoxk z.near and that $d_{\mathrm{A}}=10.0$ m and $d_{\mathrm{B}}=35.0$m. Estimate the work
done by force $F$ in moving a 2.80-kg object from $d_\mathrm{A}$ to $d_\mathrm{B}$   J

  The force on an object, acting along the x axis, varies as shown dv d 2jtj:t52e f+zu7pin Fig. 6–37. Determine the work done by this force to move the object:5efujvz2+ tdtp2j 7d (a) from x=0 m to x = 10 m    J
(b) from x = 0 m to x = 15 m    J

  A spring has $k=88$ N/m. Use a graph to determine the work needed to stretch it from $x=3.8$ cm to
$x=5.8$cm, where $x$ is the displacement from its unstretched length    J

  The net force exerted on a particle acts64gmjjh; 5so s in the $+x$ direction. Its magnitude increases linearly from zero at
$x=0$, to 24.0 N at $x=3.0$ m. It remains constant at 24.0 N from $x=3.0$ m and then decreases
linearly to zero at $x=13.0$m. Determine the work done to move the particle from $x=0$ to $x=13.0$ m
graphically by determining the area under the $F_x$ vs. $x$ graph    J

  At room temperature, an oxygen molecule, with mass9o)d oxz1f s8p of $5.31\times10^{-26}$typically has a KE of about$6.12\times10^{-21}$ J .How fast is the molecule moving?    m/s

  (a) If the KE of an arrow is doublecbb:n 60bxqoy 7:1zp/b rqdb 9d, by what factor has its speed increased? $ \sqrt{a}$ a =    (b) If its speed is doubled, by what factor does its KE increase?   

  How much work is required to ro3wd+y;6c6- 9el 4793r oasavq no4tk yjm hvstop an electron $\left(m=9.11\times10^{-31}\mathrm{~kg}\right)$ which is moving with a speed of$1. 90\times 10^{6}\mathbf{m/ s}$ ? $\boxed{a\times10^{b} \mathrm{J}}$ a =    b =   

  How much work must be done to stop a 1250-ka /3 .8tilwn2ud.wakn jv ;hk//j(wohgcar traveling at 105km/h?$\boxed{a\times10^b\text{J}}$ a =    b =   

  An 88-g arrow is fired from a bow whose string exerts an average forcya5vjj 3s )a/ge of 110 N on the arrow over a distance of 78 cm. What is the speed of the arrow as 3sayjj va/ g)5it leaves the bow?    m/s

  A baseball (m=140kg) ts8h+o5p lpx g)raveling 32m/s moves a fielder’s glove backward 25 cm when the ball is caught. What was the average force exerted by the ball on the gpl)x h+go5p8slove?    N

If the speed of a car is increased by 50%, by what faujk d3zn3x efy.j c.70q6wg)octor will its minimum braking dis fge0o 7w. yujcjdk6.zqx3n) 3tance be increased, assuming all else is the same? Ignore the driver’s reaction time.

  At an accident scene on a level road, investigators measure a car’s skid mark toh gex)9 t.+gf93wj+ck) ldoup be 88 m long. The accident occurred on a rainy day, and the coefficient of kinetic friction was estimated to be 0.42. Use these data to determine the speed of the car when the driver slammed on (and locked) the brakes. (Why does the car’s mass not matter th op +9w d+kgljugfc)9.xe)3?)    m/s

  A softball having a mahrhq9 w+up+pm93 ,xhj ss of 0.25 kg is pitched at By the time it reaches the plate, it may have slowed by 10%. Neglecting gravity, estimate the average force of air resistance during a pitch, if the distance between the plate and the pitcher is about 15 m. m 9 h,qruhxw+3ppj9h+   N

  How high will a 1.85-kg rock go if thrown straight up by someone who does 80( ;5mn yrgmf(e gg /*zyzxs0v2.0 J of work on it? Neglect air resistance. myx g/ezyf(*s 5g(zmvrg0;n 2   m

  A 285-kg load is lifted 22.0 m vertically with hr5q /kn:w j wjo,;x8zan acceleration by a single cable. Deter/hrzq j;w, xon8:5kjwmine
(a) the tension in the cable,    N
(b) the net work done on the load,    J
(c) the work done by the cable on the load,    J
(d) the work done by gravity on the load,    J
(e) the final speed of the load assuming it started from rest.    m/s

  A spring has a spring stiffness cvsct50 8857airvaxgl1oz n8 zonstant, k, of 440N/m How much must this spring betolv88 acvgirs 17z5n508xza stretched to store 25 J of potential energy?    m

  A 7.0-kg monkey swings from one bran8its3m;q ft18 bcfp ;jch to another 1.2 m higher. What is the change in potentimc3 tff18t j8q bs;;pial energy?    J

  By how much does the gravitational potential energy of a 64-kg polafjo0c9 ,yile:5z jzxsz c,o5/hiw; *e vaulter change if his center of mass rises abou cazf*i/x,jw9elsj z : oyc5;5 z0io,ht 4.0 m during the jump?    J

  A 1200-kg car rolling on a horizontal surface has speed v = 65 km/h when it st b 9qfpy94gbw+f5reyvh(1 2 agq+mu7ijc c+a,rikes a horizontal coiled spring and is brought to rest in a distance of 2.2 m. What is the spring stiffness constant of the spring y4+rq,9gv(+jghp b qceaw+c71 59ymffbu2ai?    N/m

  A 1.60-m tall person lift8/ ;w*awx) i e,zcjjkas a 2.10-kg book from the ground so it is 2.20 m above the ground. What is the poten/);wcx a jj*wz8,kae itial energy of the book relative to
(a) the ground,    J
(b) the top of the person’s head?    J
(c) How is the work done by the person related to the answers in parts (a) and (b)?    J

  A 55-kg hiker starts at an elevation of 1600 m and climbs tzs hgj 6y9w t ,ku9mld::3 k2nojer71po the top of a 3300-m peako32g1h w7up9:sjz,6ld 9:mt jn kre yk.
(a) What is the hiker’s change in potential energy?    J
(b) What is the minimum work required of the hiker?    J
(c) Can the actual work done be more than this? Explain why. ----待选择----yesno 

  A spring with k = 53N/m hangs vertically nexonbgo 4(56b s;bec4x bt to a ruler. The end of the spring is next to the 15-cm mark on the ruler. If a 2.5-kg be o45cbbsgn (b4o; 6xmass is now attached to the end of the spring, where will the end of the spring line up with the ruler marks?    cm

  Jane, looking for Tarzan, is runninj3 n/lbdj5egs f.1tlal0* m5ng at top speed (5.3m/s) and grabs a vine hanging vertically from a tall tree in dsgl bm5l*1l.e5/njjt na3 0f the jungle. How high can she swing upward?    m
Does the length of the vine affect your answer? ----待选择----yesno 

  A novice skier, starting from rest, slides down a frictionless 35.0p3v s 6hf +jd4prc31jl$^{\circ}$ incline whose vertical height is 185 m. How fast is she going when she reaches the bottom?    m/s

  A sled is initially given a shove f:bd z o7w5mz*up a frictionless 28.0$^{\circ}$ incline. It reaches a maximum vertical height 1.35 m higher than where it started. What was its initial speed?    m/s

  In the high jump, Fran’s ki96t t +cd tpa-do3h;tp/)xogu ypu nx (hy82(knetic energy is transformed into gravitational potential energy without the aid of a pole. With what minimum speed must Fran le(;xn-c3u6 yk+dt ot pua9)dh /(x2tgpth p8yoave the ground in order to lift her center of mass 2.10 m and cross the bar with a speed of 0.7m/s.    m/s

  A 65-kg trampoline artist jumps vertically upward from the top of a platfor0 gi :pvqw241.eka.tbh bmi1 rm with a speed of 5.0 m/s. (4vh1i2kbm .1tgbq.e:rp i a0w $\alpha)$ How fast is he going as he lands on the trampoline, 3.0 m below (Fig. 6-38)?$v_2$ $\approx$    m/s
(b) If the trampoline behaves like a spring with spring stiffness constant 6.2×10$^{4}$ N/m , how far does he depress it? $y_3$ =    m

  $\text{A projectile is fired at an upward angle of 45.0o from the top of a 265-m cliff with a speed of 185m/s. What will}\\\text{be its speed when it strikes the ground below?(Use conservation of energy.)}$    m/s

  A vertical spring (ignor b+zx-+m5fsrivn (m) pm*kc0ke its mass), whose spring stiffness constant is 950N/m is attached to a table and is compressed down 0.150 m. (a) What upward speed can it give to a 0.30prm 0* n-(kvx5ksf+)zibmmc+ -kg ball when released?    m/s
(b) How high above its original position (spring compressed) will the ball fly?    m

  A block of mass m slides without friction along the looped track shown iob( d;2 2dprfv3, latnn Fig. 6–39. If the block is to remain on the tracrl;pbof(ntda 2v 3d2,k, even at the top of the circle (whose radius is r), from what minimum height h must it be released?    r

A block of mass m is attached to the end of kggv4m+jern2 o ;(v6ogd* *y ra spring (spring stiffness constant k), Fig. 6–40. The blockny; m2 gk+*ro*j4g6v r god(ev is given an initial displacement $x_0$ after which it oscillates back and forth. Write a formula for the total mechanical energy (ignore friction and the mass of the spring) in terms of $x_0$ position x, and speed

  A 62-kg bungee jumper jumps from a bridge. She is tied tv3t wsa+m.ksl70o rb( o a bungee cord whose unstretched length is 12 m, and fall. 3latv(brm+ ow0s sk7s a total of 31 m. (a) Calculate the spring stiffness constant k of the bungee cord, assuming Hooke’s law applies. $\approx$    N/m
(b) Calculate the maximum acceleration she experiences. $\approx$   m/$s^2$

  The roller-coaster car shown in Fig. 6–41 is dragged up to point 1wxr lpmbct(dloj7 h09;1qs ;, where it is released from rest. Assuming no friction, calculate the speed ;ldlsj;cro1qh(t, m 9bp0 wx7 at points
2    m/s
3    m/s
4    m/s

  A 0.40-kg ball is thrown with a speed of 12 m/s at 6; puc5 jvvbr*9 vlif8an angle of 33 $^{\circ} $. (a) What is its speed at its highest point    m/s
(b) how high does it go? (Use conservation of energy, and ignore air resistance.)   m

An engineer is designing a sznt2-si-bo. 5 *q sakwpring to be placed at the bottom of an elevator shaft. If the elevator cable should break when the elevator is at a height h above the top of the spring, calculate the value that the spring stiffness constant k should have so that passengers undergo an acceleration of no more than 5.0 g when brought to rest. Let M be the total mass of the elevator and passaw -t-o s.25q*iknbzsengers.

  A cyclist intends to cycle up a wfe*95u/ckl i d os8s/7.8 $^{\circ} $ hill whose vertical height is 150 m. Assuming the mass of bicycle plus cyclist is 75 kg,
(a) calculate how much work must be done against gravity.    J
(b) If each complete revolution of the pedals moves the bike 5.1 m along its path, calculate the average force that must be exerted on the pedals tangent to their circular path. Neglect work done by friction and other losses. The pedals turn in a circle of diameter 36 cm.    N

  Two railroad cars, each of mass 7650 kg and traveling )70hfc7nrt8ufgg cx-d*; e gl 95km/h in opposite directions, c;8 0 7ge *tlgcdcgxuhfnr -7f)ollide head-on and come to rest. How much thermal energy is produced in this collision? $a\times10^b$ J a =    b =   

  A 21.7-kg child descends aty g.enz)2qu7 slide 3.5 m high and reaches the bottom with a speed of 2.2u2 7gntq.y) ezm/s How much thermal energy due to friction was generated in this process?    J

  A ski starts from rest and slidesobxi8+qws;p,8 v dp)b down a 22 $^{\circ} $ incline 75 m long.
(a) If the coefficient of friction is 0.090, what is the ski’s speed at the base of the incline? $\approx$    m/s
(b) If the snow is level at the foot of the incline and has the same coefficient of friction, how far will the ski travel along the level? Use energy methods.$\approx$    m

  A 145-g baseball is dro8tlvmj 8t 1j2jpped from a tree 13.0 m above the ground.
(a) With what speed would it hit the ground if air resistance could be ignored?    m/s
(b) If it actually hits the ground with a speed of 8m/s what is the average force of air resistance exerted on it?    N

  You drop a ball from a height of 2.0 m, and it bounces back to a height(y hy5hc7cdi2 of 1.5 m. ycdh2y5c( 7 hi
(a) What fraction of its initial energy is lost during the bounce?    %
(b) What is the ball’s speed just as it leaves the ground after the bounce?    m/s
(c) Where did the energy go?

  A 110-kg crate, starting from rest, is pulled pegrfw vvdd:u4uinw-2 **m. (across a floor with a constant horizontal force of 350 N. For the first 15 m the floor is frictionless, and for the next 15 m the coefficient of friction is 0*i :*uduv(evfmdp2gwr- w n 4..30. What is the final speed of the crate?    m/s

  Suppose the roller coaster in Fipl r;c4a01fdqxf gm)1g. 6–41 passes point 1 with a speed of If the axq1ffcag14dml0;p ) rverage force of friction is equal to one-fifth of its weight, with what speed will it reach point 2? The distance traveled is 45.0 m. $\approx$    m/s

  A skier traveling 12m/s reaches the foot oxxc3+cgy h25w6 )zhddc vdv8/ f a steady upward 18.0 $^{\circ} $ incline and glides 12.2 m up along this slope before coming to rest. What was the average coefficient of friction?   

  A 0.620-kg wood block is firmly attached to a very light horizontal spring (k=me; c*+k8ms mo180N/m) as shown in Fig. 6–40. It is noted that the block–spring system, when compressed 5.0 cm and released, stretches out 2.3 cm beyond the equilibrium position before stopping and turning back.e o+msm8*;mkc What is the coefficient of kinetic friction between the block and the table?   

  A 280-g wood block is firmly attached to a very light hpnbqgg1k/ fb1nh.:-sorizontal spring, Fig. 6–40. The block can slide along a table where the coefficient of friction is 0.30. A force of 22 N compresses the spring 18 cm. If the spring is released from this position, how far beyond its equilibrium position will it p qg.nb-bf :h1s kgn/1stretch on its first swing?    m

  Early test flights for the space shuttle used a “glider” (mass ofxfkp ob6fwl, ,v2zxp 1b81;eo 980 kg including pilot) that was launched horizontally at 500km/h from a height of 3500 m. The glider eventually landed at a speed of 200km/h (a)1b1xpe xbk,p6;v , o82f wfzlo What would its landing speed have been in the absence of air resistance?$\approx$    km/h
(b) What was the average force of air resistance exerted on it if it came in at a constant glide of 10 $^{\circ} $ to the Earth?$\approx$    N

  How long will it take a 1750-W motor to lcv iu*6 6q;wrczi :qe(ift a 315-kg piano to a sixth-story window 16.0 m 6:e wru6ic(qq ; izc*vabove?    s

  If a car generates 18 hp when traveling at a s4j,fdgtv n3+e a f h71oym.oi4teady 88km/h what must be the average force exerted on the car due to friction and air resistance? 4ij afdm4oof.hyte 7g nv+1,3    N

  A 1400-kg sports car accelerates from rest to 95km/h i 5h 1fb.s5fq.5oranll ko0xi+ ;mo5gq n 7.4 s. What is the average power delivered by the engqso;k n5m1 lg.o5aihf l .xfo+r05bq5ine?$\approx$    hp

  (a) Show that one British horsepowerhgbss:wmfdw9 s4h)5j z gv, 63ob0k*l$ \mathrm{ft}\cdot\mathrm{lb/s}$ is equal to 746 W.
(b) What is the horsepower rating of a 75-W light bulb?    hp

  Electric energy units are often expressed ip:b2az w*hw t,n the form of “kilowatt-hours.”
(a) Show that one kilowatt-hour (kWh) is equal to $3.6\times10^6$J
(b) If a typical family of four uses electric energy at an average rate of 520 W, how many kWh would their electric bill be for one month $\approx$   kW*h
(c) how many joules would this be?$a\times10^b$ J a =    b =   
(d) At a cost of 0.12 dollars per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?    dollars

  A driver notices that her 1150-kg car slows down from to 65km/h ib) n:-w*fxfl wn about 6.0 s on the level when it is in neutral. Approximately what power (watts and hp) is needed to keep the carnbl* xw )f-:wf traveling at a constant 75km/h.    hp

  How much work can a 3.0-hp motor do in 1gmg 46eq*r-..lw rqs,+bwcu n.0 h? $a\times10^b$ J a =    b =   

  A shot-putter accele6ye;sc-4 pz barates a 7.3-kg shot from rest to 14m/s If this motion takes 1.5y;eb 4spa -cz6 s, what average power was developed?$\approx$    W

  A pump is to lift 18.0 kg of water per minute through a height of 3j9eg5:u; fav u.60 m. What oua fv9eu:j5ug ;tput rating (watts) should the pump motor have?    W

  During a workout, the football players at State Urz 2xmz+7 naoo vcd .sn1, 3/ygdn.0zj. ran up the stadium stairs in 66 s. The stairs are 140 m long and inclined at an angle y1zc m+ar.n7,o0z v.2zj sdd o 3g/nnxof 32 $^{\circ} $. If a typical player has a mass of 95 kg, estimate the average power output on the way up. Ignore friction and air resistance.    W

  How fast must a cyclist climb a 6.0 y3pw)t/ b pmm4$^{\circ} $ hill to maintain a power output of 0.25 hp? Neglect work done by friction, and assume the mass of cyclist plus bicycle is 68 kg.   m/s

  A 1200-kg car has a maximum power outputsqohudf t(f66ueu8vl6 5 .r w- of 120 hp. How steep a hill can it climb at a constant speed of 75km/h if the frictional forces add up to efro qw-68dfu5 l( uu6v sh.t6650 N?    $^{\circ} $

  What minimum horsepower must a motor have to be able to drag a 310-kg bohh)vmhs 0f 5k4x along a level floo vhm5f4skh) 0hr at a speed of 1.2m/s if the coefficient of friction is 0.45?    hp

  A bicyclist coasts down7 wf+cor76 u 4jnajb qw1+ezd/ a 7.0 $^{\circ} $ hill at a steady speed of 5m/s Assuming a total mass of 75 kg (bicycle plus rider), what must be the cyclist’s power output to climb the same hill at the same speed?    W

  Designers of today’s cars have built “5mi/h(8km/h) bumpers” that aew1*ss2cw0uw gu0z; m re designed to compress and rebound elastically without any physi c w;0u0w s*ezmug12wscal damage at speeds below 8km/h If the material of the bumpers permanently deforms after a compression of 1.5 cm, but remains like an elastic spring up to that point, what must the effective spring stiffness constant of the bumper be, assuming the car has a mass of 1300 kg and is tested by ramming into a solid wall? $a\times10^b$ N/m a =    b =   

  In a certain library t8t 9;qvsv2bfdhe first shelf is 10.0 cm off the ground, and the remaining four shelves are each spaced 30.0 cm above the previous one. If the average book has a mass of 1.5 kg with a height of 21 cm, and an average shelf holds 25 st9 fdqb; 82vvbooks, how much work is required to fill all the shelves, assuming the books are all laying flat on the floor to start? $\approx$    J

  A film of Jesse Owens’s famouo-: lbbh rw1p7 8jmgm5 rxgy or24-jc;s long jump (Fig. 6–42) in the 1936 Olympics shows that his center of mass rose 1.1 m from launch point to the top of the arc. What minimum speed didy-ormmjjc-5r rb8;xg g4 72b wp1ol:h he need at launch if he was traveling at 6.5m/s at the top of the arc?   m/s

  The block of mass m sliding without friction7vzxh eb4q l7.h10fab along the looped track shown in Fig. 6–39 is to remain on the tracxhf4 .7zb70aeqlvh1 bk at all times, even at the very top of the loop of radius r.
(a) In terms of the given quantities, determine the minimum release height h (as in Problem 40). Next, if the actual release height is 2h, calculate    r
(b) the normal force exerted by the track at the bottom of the loop,    mg
(c) the normal force exerted by the track at the top of the loop,   mg
(d) the normal force exerted by the track after the block exits the loop onto the flat section.   mg

  An airplane pilot fell 370 m after jumping from an aircraft withob)lxe gi ;9bpkbn;t .5ut his parachute opening. He landed in a snowbank, creating a crater 1.1 m deep, but survi 5b9bk .)xt;;ng bpleived with only minor injuries. Assuming the pilot’s mass was 78 kg and his terminal velocity was 35m/s estimate
(a) the work done by the snow in bringing him to rest; $\approx$    J
(b) the average force exerted on him by the snow to stop him;$\approx$    N
(c) the work done on him by air resistance as he fell.$\approx$    J

A ball is attached to a horn1vd8sdji 7+r63ik /mwd:z rsizontal cord of length L whose other end is fixed (Fidnmrsiij1w d7v r+dz6/sk8:3g. 6–43).
(a) If the ball is released, what will be its speed at the lowest point of its path?
(b) A peg is located a distance h directly below the point of attachment of the cord. If h=0.8L what will be the speed of the ball when it reaches the top of its circular path about the peg?

  A 65-kg hiker climbs to the top of a 3700-m-high mountain. The climb is made injvxcd q60 6gs(h5j+m yb 4rcn9sj6hi/ 5.0 h starting at an elevation of 2 jjqib6+cm0h4r5 v /dg96yxhcjn s6(s300 m. Calculate
(a) the work done by the hiker against gravity,   
(b) the average power output in watts and in horsepower,   W    hp
(c) assuming the body is 15% efficient, what rate of energy input was required.    hp

  An elevator cable breaks when a 920-kg elevator is 28 m above a hugww6x 5ajt1 0 jy4g-nj5ru x.xze spring ($k=2.2\times10^{5} \mathrm{N/m}$) at the bottom of the shaft. Calculate
(a) the work done by gravity on the elevator before it hits the spring,$\approx$    j
(b) the speed of the elevator just before striking the spring,$\approx$    m/s
(c) the amount the spring compresses (note that work is done by both the spring and gravity in this part).    m

  Squaw Valley ski area in California claims that its liqden6 9z pf7(358 inhhmgkic6fts can move 47,000 people per hour. If the average lift carries people about 200 m (vertically) higher, estimatez hde6(g5hcm7k6p n3n iq9f8i the power needed.$a\times10^b$ W a =    b =   

  Water flows over a dam at the rate of 650kg/s and fa3v*yxyt m 32hfaske al v8((s:lls vertically 81 m before striking the turbine blades. Calculat2(m vtx y(sa 3s yh8k:aef3lv*e
(a) the speed of the water just before striking the turbine blades (neglect air resistance), $\approx$    m/s
(b) the rate at which mechanical energy is transferred to the turbine blades, assuming 58% efficiency.    W

  Show that on a roller coaster with a circulgy ot-fci1;xl;,dj +z ar vertical loop (Fig. 6–44), the difference in your apparent weight at the top of the circular loop and the bottom of the circular loop is 6 g’s — that is, six times your weight. Ignore friction. Shxy tz1+df;gljc-;i,oow also that as long as your speed is above the minimum needed, this answer doesn’t depend on the size of the loop or how fast you go through it.    mg

  (a) If the human body could convert ;/ s tro:, d :lvzhc(znwo7yx8a candy bar directly into work, how high could an 82-kg man climb a ladder if he were fueled by one bar (=100 :8t:zn d;w(h oo/rxzlyv c,7s0kJ)    m
(b) If the man then jumped off the ladder, what will be his speed when he reaches the bottom?    m/s

  A projectile is fired at an upward angle ofq juw7nqk.b ),la9f*v 45.0$^{\circ} $ from the top of a 165-m cliff with a speed of 175m/s What will be its speed when it strikes the ground below? (Use conservation of energy and neglect air resistance.)    m/s

  If you stand on a bathroom scale, the spring inside the scale compress tf;j q1s+lbch *62sizes 0.60 mm, and it tells you your weight is 710 N. Now if you jump on the scale from a height of 1.0 m, what does the scaqs zslct;fj6+bi*1 h 2le read at its peak?    N

  A 65-kg student runs at 5m/s grabs6k ek;bm(5e ,zskdfe9+n/hcu a rope, and swings out over a lake (Fig. 6–45). He releases kef(z dh;,ee+69mbckn sk 5/ uthe rope when his velocity is zero.
(a) What is the angle when he releases the rope?    $^{\circ} $
(b) What is the tension in the rope just before he releases it?    N
(c) What is the maximum tension in the rope?    N

  In the rope climb, a 72-kg athlete climbs a vertical distance of 5.0 m in 9xhu end+3g+kx;r.8p p.0 s. What minimum power output was used to accompl.g8up +ndhk +xe x3;prish this feat?    W

  Some electric-power companies use water to store energy1brcue7 3ok 5p. Water is pumped by reversible turbine pumps from a low to a high reservoir. To stooeruc3b k 175pre the energy produced in 1.0 hour by a 120-MW ($120\times10^{6}$W) electric-power plant, how many cubic meters of water will have to be pumped from the lower to the upper reservoir? Assume the upper reservoir is 520 m above the lower and we can neglect the small change in depths within each. Water has a mass of 1000 kg for every 1$m^3$.    $m^3$

  A spring with spring stiffness constan+ihj2ja f4 yo)t k is cut in half. What is the spring stiffness constant for each of the two resu4o+j2ijhaf y )lting springs?   k

  A 6.0-kg block is pushed 8.0 m up a rougiau:a rg 7z)eh wd2y2lahs8) 4h 37 $^{\circ} $ inclined plane by a horizontal force of 75 N. If the initial speed of the block is 2.2m/s up the plane and a constant kinetic friction force of 25 N opposes the motion, calculate
(a) the initial kinetic energy of the block; $\approx$    J
(b) the work done by the 75-N force; $\approx$    J
(c) the work done by the friction force;    J
(d) the work done by gravity;$\approx$    J
(e) the work done by the normal force;    J
(f) the final kinetic energy of the block.$\approx$    J

  If a 1500-kg car can accelera +0z t/pk;bpqtte from 35km/h to 55km/h in 3.2 s, how long will it tbpt ;+ t/q0kpzake to accelerate from 55km/h to 75km/h Assume the power stays the same, and neglect frictional losses.    s

  In a common test for cardiac fug vkk8t65x987zb ufku nction (the “stress test”), the patient walks on an inclined treadmill (Fig. 6–46). Estig875k vbk xtuf68uz 9kmate the power required from a 75-kg patient when the treadmill is sloping at an angle of 15 $^{\circ} $ and the velocity is 3.3km/h (How does this power compare to the power rating of a light bulb?)$\approx$    W

  (a) If a volcano spews a 500-kg rock verzd jj 92 1whba2e*qc9atically upward a distance of 500 m, whatzc hjq a 9a1db2*9ew2j was its velocity when it left the volcano? $\approx$    m/s
(b) If the volcano spews the equivalent of 1000 rocks of this size every minute, what is its power output? $\approx$ $a\times10^b$ W a =    b =   

  Water falls onto a water wheel from a hei(rhmr2cr ox:fkei*jeh73* ;j ,4gstt ght of 2.0 m at a rate of 95kg/s (a) If this water wheel is set up to provide electricity output, wha*(t c4 jrmije,:372eh; kfrhrtosx* gt is its maximum power output?    W
(b) What is the speed of the water as it hits the wheel?    m/s